In arctic and subarctic regions, rapid climate changes enhance biogenic volatile organic compound (BVOC) emissions from vegetation, with potentially significant influence on atmospheric processes. However, the seasonal and diel patterns of bidirectional exchange (flux) of BVOCs remain poorly studied in these regions. Here, we deployed a proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) to investigate ecosystem-level BVOC fluxes over a growing season in a subarctic tundra heath in Abisko, Northern Sweden, and to quantify BVOC emissions from two widespread dwarf shrubs in the high latitudes, Salix myrsinites and Betula nana. As expected, ecosystem fluxes of short-chained oxygenated compounds (e.g., methanol, acetaldehyde and acetone) and terpenoids (e.g., isoprene, monoterpenes and sesquiterpenes) followed different seasonal and diel patterns. For the short-chained oxygenated compounds, net emissions dominated and peaked in the early growing season, while net deposition occurred sporadically, particularly at night. In contrast, terpenoids were almost exclusively emitted from the ecosystem, with maxima occurring in the peak growing season. At the branch level, these compound groups were emitted from both S. myrsinites and B. nana in clear diel patterns with high emissions during the day. S. myrsinites was dominated by isoprene emissions whilst B. nana was dominated by terpene emissions. Methanol, acetaldehyde and acetone were emitted at comparable levels and similar patterns from both species. Both ecosystem fluxes and branch emissions responded exponentially to enclosure temperature and depended on light levels. Compared to the BVOC emission models, however, the temperature responses were steeper for isoprene, monoterpenes, methanol and acetone, but weaker for sesquiterpenes. Apart from the well-known compounds, many other BVOCs, such as some carbonyls and nitrogen-containing compounds, were emitted from both the ecosystem and plants with significant contributions to the season variation in ecosystem fluxes. Overall, our study highlights the complexity of subarctic ecosystem BVOC fluxes, which vary both seasonally and diurnally. Vegetation composition changes triggered by climate change will shift BVOC composition, with important implications for atmospheric processes and local climate.

Plant volatile organic compound (VOC) emissions can drive important climate feedbacks. Although mosses and lichens are important components of plant communities, their VOC emissions are poorly understood. It is crucial to obtain more knowledge on moss and lichen VOCs to improve ecosystem VOC emission models. This is especially relevant at high latitudes, where mosses and lichens are abundant and VOC emissions are expected to increase in response to climate change. In this study, we examined VOC emissions from four common moss (Hylocomium splendens, Pleurozium schreberi, Sphagnum warnstorfii, and Tomentypnum nitens) and lichen (Cladonia arbuscula, Cladonia mitis, Cladonia pleurota, and Nephroma arcticum) species in the Subarctic using gas chromatography-mass spectrometry (GC-MS) and proton-transfer-reaction time-of-flight mass spectrometry. Moss and lichen VOC emissions were dominated by low molecular weight (LMW) VOCs, such as acetone and acetaldehyde, as well as hydrocarbons (HCs) and oxygenated VOCs (oVOCs). Of the studied mosses, S. warnstrofii had the highest and H. splendens had the lowest total VOC emission rates. The VOC emission blends of P. schreberi, S. warnstrofii, and T. nitens were clearly distinct from one another. Of the lichens, N. arcticum had a different VOC blend than the Cladonia spp. N. arcticum also had higher emission rates of HCs, oVOCs, and other GC-MS-based VOCs, but lower LMW VOC emission rates than the other lichen species. Our study demonstrates that mosses and lichens emit considerable amounts of various VOCs and that these emissions are species dependent.

Aerosol particles were collected at the Zeppelin Mountain Atmospheric Research Station (474 m asl) near Ny Alesund (Svalbard, Norway) on 27 different days between July 2007 and December 2008. The size, morphology and chemical composition of 57,617 individual particles were studied by high-resolution scanning electron microscopy and energy-dispersive X-ray microanalysis. Based on chemical composition, morphology, mixing state and stability under electron bombardment, the particles were assigned to one of the following groups: sea salt, aged sea salt, Ca sulphates, Na sulphates, carbonates, soot, silicates, fly ashes, secondary aerosol, secondary aerosol plus sodium, secondary aerosol plus soot, mixed particles and others. Sea salt, aged sea salt, silicates and mixed particles (mixtures of sea salt, silicates and Ca sulphates) are the most abundant groups for particles with aerodynamic diameters > 0.5 mu m, secondary aerosol, mixed particles and secondary aerosol with soot inclusions below 0.5 mu m. Silicate fly ashes (major source coal burning) and metal fly ashes (from metallurgical high temperature processes) occur only at very low number concentrations. In contrast to previous work, the fly ash abundance is not correlated with air masses that crossed industrialized regions in Central and Eastern Europe, Scandinavia or Russia. These observations indicate a significant reduction of long-range transport of heavy metals to Svalbard. Soot (external and internally mixed with secondary aerosol) shows a pronounced seasonal pattern with a much lower abundance during summer compared to spring, autumn and winter. The soot abundance is not correlated with the air mass back-trajectories. During summer (July and August), soot was only observed when cruise ships were present in the area around Ny Alesund (Kongsfjorden). Pronounced seasonal patterns were observed for the abundance of the mineral dust component which is generally lower in summer compared to the other seasons. The observed seasonal dependence of anthropogenic primary particles (soot, fly ashes) is in good agreement with the Arctic circulation pattern. (C) 2011 Elsevier Ltd. All rights reserved.

The atmospheric evolution of eight non-methane hydrocarbons (ethane, acetylene, propane, n-butane, isobutane, n-pentane, isopentane and benzene) and five alkyl nitrates (2-propyl, 2-butyl, 3-methyl-2-butyl and the sum of 2+3-pentyl nitrates) are reconstructed for the latter half of the 20th century based on Arctic firn air measurements. The reconstructed trends of the non-methane hydrocarbons (NMHCs) show increasing concentrations from 1950 to a maximum in 1980 before declining towards the end of last century. These observations provide direct evidence that NMHCs in the northern hemisphere have declined substantially during the period 1980-2001. Benzene concentrations show a smaller increase between 1950 and 1980 than the other NMHCs indicating that additional sources of benzene, other than fossil fuel combustion, were likely important contributors to the benzene budget prior to and during this period. The declining benzene concentrations from 1980 to 2001 would suggest that biomass burning is unlikely to be important in the benzene budget as biomass burning emissions were reportedly increasing over the same period. Methyl and ethyl nitrate show growth patterns in the firn that suggested perturbation by in-situ production from an unidentified mechanism. However, the higher alkyl nitrates show evidence for increasing concentrations from 1950 to maxima in the mid 1990s before decreasing slightly toward the end of the last century. The differing atmospheric evolution of the alkyl nitrates relative to their parent hydrocarbons indicate an increase in their production efficiency per hydrocarbon molecule. Using a steady state analysis of hydrocarbon oxidation and alkyl nitrate production and loss we show that reactive nitrogen oxide (NOx) concentrations in the northern hemisphere have likely increased considerably between 1950 and 2001. (C) 2012 Elsevier Ltd. All rights reserved.